Electric heater



May 28, 1935-. L, M, DALY 2,003,176

ELECTRI C HEATER Original Filed Aug. 12, 1935 zo z/ 2a 32 Inventor: Loretta M. Daig,

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Patented May 28, 1935 UNITED STATES PATENT OFFICE ELECTRIC HEATER Loretta M. Daly, Pittsiield, Mass., assignor to General Electric Company, a corporation of New York 1 Claim.

My invention relates to electric heaters and the like, and it has for its object the provision of improved means for sealing the terminals of heaters of this type.

Although not limited thereto, my invention has particular application to electric heaters of the encased or sheathed type, such as described and claimed in the United States Patent No. 1,367,341 to C. C. Abbott, dated February 1, 1921. As there described, heaters of this type comprise a resistance conductor embedded in an insulating material and enclosed by an outer metallic protec tive casing.

In one of its aspects, my invention contemplates the provision of improved means for sealing the terminals of electric heaters of this type whereby the heaters are rendered impervious to moisture, oil, gas, and like fluids.

In carrying my invention into effect in one form thereof, I surround each terminal of the heater with an insulating body formed of some suitable material, such as porcelain. This body may be in the form of a sleeve that is provided with an aperture for receiving the terminal. The insulating sleeves are received in metallic cupshaped casings that are applied to the ends of the sheath, and metallic fluid impervious joints are provided between the sleeves and the casings, as well as between the sleeves and the terminals to which the sleeves are applied. Also, fluid-tight joints are provided between the casings and the sheath.

This application is a division of my copending application, Serial No. 684,839, filed August 12, 1933.

For a more complete understanding of this invention, reference should be had to the accompanying drawing in which the single figure is a fragmentary elevation of a sheathed electric heater provided with a terminal seal arranged in accordance with my invention, portions of the heater being shown in section so as to illustrate certain details of construction.

Referring to the drawing, I have shown my invention as applied to a helical coil sheathed electrical heating unit of the type described and claimed in the above-mentioned Abbott Patent No. 1,367,341.

As shown, this heating unit comprises a helical resistance conductor l embedded in a compacted mass of powdered heat refractory electrically insulating material H, the conductor and insulating material being encased by a metallic sheath l2.

The resistance conductor ll) extends through (Cl. 201-6'l) a considerable portion of the length of the sheath l2 and has its two ends connected to terminal members I3 (only one of which is shown), which members project from the ends of the sheath.

While the resistance conductor l0 may be con- 5 nected to its terminals l3 in any suitable manner, I prefer to connect them in the fashion described and claimed in United States Patent No. 1,494,936 to C. C. Abbott, dated May 20, 1924. As there described, each terminal member l3 has its inner ends threaded and is electrically and mechanically connected with the resistance conductor ill by screwing a number of the end turns of the conductor onto the threaded end of the terminal.

In making the heating unit thus far described, the terminals l3 are attached to the conductor Ill in the manner described, and then the conductor with the terminals attached is threaded through the sheath l2. The sheath is then loaded with the magnesium oxide H in any suitable manner, and then its diameter is reduced, as by swaging or by rolling, so as to highly compact the magnesium oxide.

In order to render the heater impervious to the passage of fluids through the terminals, I surround each terminal with a layer or a sleeve [4 formed of some suitable electrically insulating material, such as porcelain. The porcelain sleeve It, as shown, is provided with a centrallyarranged aperture l5 for receiving the terminal 13.

A cup-shaped casing or receptacle i6 is used to receive each insulating sleeve. As shown, the cylindrical casing IE is fitted t0 the end portion of the sheath l2. The cup 16 is secured to the sheath 2| by means of a brazed joint ll which provides a fluid-tight connection between these members. The terminal l3 passes through the cup l6 and extends for some distance beyond the mouth of the cup. As shown, the sleeve It is inserted in the mouth of the cup. Preferably, the mouth of the receptacle I6 will be tapered, as indicated at I8, the taper terminating in a seat IQ for receiving the insulator. The insulator preferably will be formed with a tapered portion 20 which extends for some distance into the receptacle l6, and the insulator will be provided with a ledge 2| which rests upon the seat or shoulder IS. The projecting portion 20 increases the electrical creepage space between the terminal I3 and the metallic casing l6 and sheath l2.

Fluid-tight metallic joints are provided between the insulator and the receptacle [6 and between the insulator and the terminal l3. For this purpose, the insulator I4 is provided with a band of metal 22 surrounding that portion of the insulator which is received within the recess l8. As shown, this metallic band 22 has a width substantially equal to the depth of the recess. This metal coating is applied to the insulator in any suitable manner. Thus, the band may be formed by any well-known metallizing process. For example, if the layer of metal be formed of platinum, and this is a preferred metal, the layer may be applied by any well-known platinizing process. The important feature is that the metal be applied by some method which will practically integrally unite the metal with the porcelain sleeve l4, and that the metal applied be of such a character that it can be united with the terminal l3 and the metal cup 16.

The coating 22 on the insulator is soldered to the walls of the receptacle so as to form a fluidimpervious metallic joint 23 between these members.

The outer end surface of the insulator is provided with a metallic coating 24 substantially covering this surface of the insulator. This coating 24 is soldered to the terminal 13 so as to provide a fluid-impervious metallic joint 25 between these members. 7

It will be observed that the receptacle I6 is connected to the sheath l2 by means of the fluidtight joint I 1, while the insulating sleeve I4 is connected to the receptacle l6 by means of the fluid-tight joint 23 and with the terminal by the fluid-tight joint 25.

It will be understood that any suitable terminal connector (not shown) may be secured to the portion of the terminal I3 that projects from the insulating sleeve l4.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications maybe made, and I, therefore, contemplate by the appended claim to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

An electric heater comprising a resistance conductor, a metallic sheath encasing said conductor, a terminal connected with said resistance conductor having a portion projecting from said sheath, a metallic casing surrounding said terminal positioned in spaced relation with it, a fluidtight joint between said casing and said sheath, an electrically insulating sleeve surrounding said terminal and received in said casing, a metallic band surrounding a portion of said sleeve within said metallic casing and rigidly secured to said sleeve, a metallic layer covering the outer surface of said sleeve rigidly secured to the sleeve, and metallic masses united into substantially homogeneous structures with said metallic band and the inner walls of said metallic casing and with said metallic layer covering the outer surface of said sleeve and said terminal, whereby a fluidtight joint is effected between said terminal and said metallic casing.

LORE'I'IA M. DALY. 

